SUMMARY Bacterial vaginosis (BV) is associated with higher risks of a dozen or more serious health complications. Unfortunately, antibiotic treatment is only effective for temporarily alleviation of BV. Microbiological and biochemical signatures of BV have been studied at length in relation to the `healthy' vaginal microbiome dominated by lactobacilli. However, little is known about the metabolism of many fastidious vaginal bacteria, how the metabolism of carbohydrates may drive bacterial growth, or how metabolic function of different bacteria may drive the compositions of bacterial communities and the physiology of the vagina. Such gaps in our understanding prevent the development of rational strategies to deter BV bacteria and encourage lactobacilli in the vagina. This proposal uses new experimental models of human vaginal community dynamics with the overarching goal of defining the carbohydrate preferences of vaginal bacteria. By measuring the growth and metabolic output of bacteria in mono-culture, and within ex vivo vaginal microbial communities, our broader objective is to develop conditions that specifically discourage BV bacteria and favor lactobacilli. In three specific aims, this proposal will use a combination of tools in microbiology and biochemistry together with genomics and proteomics to investigate the carbohydrate preferences of vaginal bacteria and potential mechanisms that can change in the composition and metabolism of vaginal communities. Glycogen is one example of an abundant potential source of carbohydrates in the vagina. As a polymer of glucose, glycogen is believed to be a carbon source for `healthy' lactobacilli. However, this interpretation has been based largely on correlative data rather than experimental investigation of the metabolic behaviors of vaginal bacteria. We present evidence that glycogen metabolism can fuel the outgrowth of specific BV bacteria and can lead to depletion of glycogen in culture. In Aim 1, we will examine which bacteria found in the vagina can employ amylases to metabolize glycogen, and we will define the relevant biochemical activities and identities of glycogen-cleaving enzymes. In Aim 2, we will investigate the larger role of glycogen metabolism for vaginal community dynamics, testing the hypothesis that glycogen supports the growth of bacteria in cultured BV communities, and that the inhibition of glycogen metabolism limits the expansion of BV-associated bacterial communities. Finally, in Aim 3, we will comprehensively investigate the carbohydrate preferences of vaginal bacteria, with particular emphasis on selectively promoting the growth and metabolism of lactobacilli. The successful completion of these aims will have an important positive impact on this field by establishing mechanistic insights about how BV bacteria utilize potential carbohydrate carbon sources available in the vagina. Furthermore, successful completion of these studies will lead to important insights about how to use the carbohydrate preferences of beneficial lactobacilli to promote their growth in the vagina, modulating carbohydrate metabolism for the treatment of BV.